Antenna



Nov. 7, 1933. c, sgr-'RANKLIN ANTENNA Filed Jan. 24, 1929 Neg/f5 nvemoz mms s FRANKLIN NS wmWj/Q/MM Patented Nov. 7, 1933 UNITED STATES ANTENNA Charles Samuel Franklin, London, England, as-

signor to Radio Corporation of America, a corj poration of Delaware Application January 24, 1929, serial N0.`33,4,632, and in Great Britain February 2, 1928 6 claims. (C1. 25o-33) .This invention relates to aerial systems, and more particularly to reflecting aerial systems of the kind comprising a plurality .of tuned conductors arranged, for example, in a plane or as a parabola for the purpose of giving enhanced directional properties.

According to this invention an aerial system comprises a plurality of multi-conductor elements each having a ratio of inductance to radiation resistance less than that obtainable by a single conductor. Such `multi-conductor elements may be formed as cages or grids, of wires or rods. f

It is found that the. use of multi-conductor v elements in accordance with this invention results in greater efficiency than is obtainable with the single conductors hitherto employed, while the tuning is rendered less critical andan aerial system therefore rendered operable over a wider wave band than has hitherto been possible.

Aerial systems comprising multi-conductor elements in accordance with this invention may be built up of a plurality of aerial units, spaced a fraction of `a wave length apart, each such lunit consisting of a number of tuned multi-conductor elements located above one another and insulated from one another. Alternatively, thek said elements may all be connected directly in series through inductance coils or their equivalents in a manner similar to that already proposed in known aerial systems, so that the elements act as reectors and radiators,.while the coils or their equivalents are of comparatively small reflecting or radiating power. A

The invention is explained in connection with and illustrated by the accompanying drawing, in which Figure 1 illustrates an antenna section employing simple reflector conductors; Figure 2 illustrates the use of double reflector conductors; Figure 3 shows the use of cage reflector conductors; and Figure 4 is a graph explanatory of my invention.

Referring to Figure l, which shows a known aerial 'and reflector system, A. represents an aerial of the kind described in the specification of British Patent No. 242,342, and which is energized from a distant transmitter (not shown) through a feeder F. Located substantially one quarter of a wave length in rear of the aerial A is a reector R consisting of three rods or wires, each one half wave length long, situated above and insulated from one another.

With this arrangement currents are induced in the reflector rods by radiation from the aerial fleeting elements.

A, and, provided that the said reflector is in tune with the transmitted Wave, these currents will be in phase with the inducing voltage. There will thus be obtained from kthe combination of aerial and reflector aradiated field having a maximum intensity in front of the aerial in a` direction away from the reflector and a minimum intensity in the opposite direction, the said minimum, however, never reaching zero owing to the eiect of the ohmic resistance ofthe re- Ify the radiated fields be measured-at appreciable distances in front of and behind the whole system `it will be found that the intensity of radiation in rear'of the system is greater at frequencies different from the resonant frequency of the reflector-'an effect which may be explained by the fact that when the transmittedfrequency is not equal to the resonant frequency of the reiiector, the currents induced therein are neither sufiiciently large nor in correct phase to give a minimum radiation as low as that obtained at resonance.

If, now, in accordance with the present invention, multi-conductor elementsare, as shown, for example inFigures 2 and 3, substituted, for the single conductor elements in the reflector, a very considerable improvement results. yIn' Figure 3 cages of conductors are substituted for `the single conductors'shown in Figure l. These may be separated by insulators, 2, or phase reversing reactances, 3, both being shown in Figure 3, by way of example. f i

It will be understood, of course, that in the case of Aeach of the illustrated arrangements the complete antenna may comprise a large number of antenna sections, such as have been illustrated, positioned transversely of the direction of desired communication, and coupled cophasally to a transmitter or a receiver, or, if preferred, a single antenna conductor surrounded by a parabolic formation of reflectorconductors, and further, that -a greater or lesser number of superposed half wave length units may be employed.

Such cages or grids of wires, while having substantially the same radiation resistance as single wire elements,are of considerably lower inductancek and resistance, and in consequence, at frequencies a given distance removed from the resonant frequency of the reflector, the currents induced therein are larger and more nearly in phase than those which would be obtained with the known single wire element reflectors, the result being that the field of radiation in rear of the reilectors is of smaller intensity.

This improvement is shown graphically in Figure 4, by means of curves whose ordinates are ratios of field intensities in rear of a reflector to ance with this invention may be connected together in series by means of inductance coils or equivalent devices of small radiating or refiecting power.

Multiple conductor aerial systems in accordance with this invention are applicable with advantage not only to refiecting aerial systems but also to transmitting aerial systems. With such application, the advantage obtained is not an improved directional effect but the fact that the aerial will accept power from a feeder system over a wider band of frequencies, v

As is explained in the specification of British Patent No. 281,762, the impedance of a wire, long compared with a given energizing wave length, varies (as the length of the wire increases) between maximum and minimum limiting values; or, alternatively, the impedance of a given wire or aerial varies between maximumand minimum limits as the energizing wave length is varied. By employing multiple conductor aerials in accordance with this invention, the separation of these limiting values is reduced, compared to that which obtains with a known single Wire element aerial.v The rate of change of impedance with respect to change of energizing frequency is therefore also reduced and in consequence, a multiple conductor aerial, which has been adjusted in known manner to` accept energy atfal given frequency through a transformer or the like from a feeder, will accept that energy within specified limits over a wider range of frequencies than would an otherwise similar aerialmade up of singlewire elements; in other words the multiple conductor aerial will accept the same amount of energy at a frequency'a given amount different from the design frequency,I as will the single conductor element aerial at a frequency nearer the design frequency.

Having now particularly described and'ascertained the nature of my said inventionand in what manner the same is to be performed, I declare that what I claim l. A unidirectional antenna comprising a plurality of antenna conductors each approximately a half wave in length and connected end to end by substantially non-radiating phase reversing reactances, and a plurality of reflector conductors each approximately'a half Wave in length spaced approximately an odd number of quarter wave lengths away from the antenna conductors and comprising structurally a group of closely adjacent directly connected parallel conductors, connected end to end by insulating means.

2. A unidirectional antenna comprising a plurality of antenna conductors each approximately a half Wave in length and connected end to end by substantially non-radiating phase reversing reactances, and a plurality of reflector conductors each approximately a half wave in length spaced approximately an odd number of quarter Wave lengths away from the antenna conductors and comprising structurally a group of closely adjacent directly connected parallel conductors, connected end to end by substantially non-radiating phase reversing reactances.

3. AA unidirectional antenna comprising a plurality of vertical antenna conductors each approximately a half wave in length and connected end to end by substantially non-radiating phase reversing reactances, and a plurality of vertical reiiector conductors each approximately a half wave in length spaced approximately7 an odd number of quarter wave lengths away from the antenna conductors and comprising structurally a group of closely adjacent directly connected parallel conducors, connected end to end by insulating means.

4. In a communication system the'combination With a multi-sectional aerial of a vertical reflecting system having a length a multiplev of half the length of the communication wave compris- 'ing a'plurality'of substantially half wave length multi-conductor elements insulated from each other, each element having a ratio of inductance to radiation resistance less than that of a single conductor. f 5. In a communication system the combination with a multi-sectional aerial having radiating sections in a straight line each of which is at least equal to half the length of the communication; Wave, of a plurality of separated reflector arrangements placed end to enel, each of the latter beingr individual to' one Aof said radiating aerial sections and located approximately an cdd multiple of a quarter wave length away from said sections, each of said reflectors comprising 'a plurality of adjacent directly connected parallel conductors.

6. In a communication system the combination with a multi-sectional aerial,` having radiating sections in a straight line each of which isat least equal to half the length ofthe communication Wave, of a plurality of separatedA reiiector tions-and comprising multi-conductor elements having a ratio of inductance to radiation resistance less than that of a single conductor.

CHARLES SAMUEL FRANKLIN. 

